The increasing cost pressure in the pulping and other biomass utilizing industry as well as the increasing awareness of the problems related to fossil oil based products has led to the search of new renewable raw materials for energy and material applications. The use of for example renewable and easily degradable packaging films or fuels produced from wood sugars could result in significant decreases of the carbon footprint of these industries. Today's pulping processes give rise to discharges of oxygen demanding substances, which are normally taken care of in biological purification of the outlet water. It is costly to build such purification plants.
Lignocellulosic materials are complex structures consisting of a multitude of different kind of molecules that are bound to one another with chemical bonds. This causes significant problems in the fractionation, upgrading and the use of the molecules. There is no broad consensus among researchers about the existence of natural covalent bonds between lignin and hemicelluloses in wood. An often used view is that these bonds are formed during the processing of the molecules. Some new research data however have suggested that aromatic structures are covalently bound to cellulose and hemicelluloses through ester-, ether- or phenyl glucosidic bonds. This was reported by for example Iawoko and coworkers, Holzforschung, Vol 60, pp. 156-161, 2006.
Two types of phenolic polysaccharides are well known and characterized. Ferulated arabinoxylans have ferulic acid moieties attached to the polysaccharides and they are known to be present in grasses and cereals. Phenolic pectins can be found i.e. from beet pulp. It is also known that polysaccharides can be derivatized with e.g. aromatic compounds.
Barrier films are used in packaging to increase the shelf life of the product by keeping it away from odors, oxygen gas etc. Petroleum based and aluminum films are dominating the field but films made of renewable materials have gained a lot of interest in latest years. Starch based films are the most widely applied renewable polymers for this purpose but they are based on food based resources.
Different branched and non-branched polysaccharides (including but not limited to hemicelluloses) are together with lignin and cellulose the main constituents of wood (as well as many other lignocellulosic materials). They have been shown great potential as raw material for material and chemical applications as well as a feedstock for fermentations. Wood hemicelluloses such as mannans and xylans can be isolated from the process waters of mechanical pulping or from a pre-hydro lysis process with a price that is competitive with the petrochemical based equivalents. Considering the large size of this industry worldwide, it can be said that these hemicelluloses are available in great amounts, further advantages for the use of this raw material source include the renewable nature of the material as well as the fact that this material source is not part of the food production. Drawbacks of the hemicelluloses derived from these processes are that their molecular weight is very low and they exist in complex mixtures with other compounds in the process waters.
The international patent application WO 97/17492 describes a way to prepare a pulp strengthening agent and its addition to a lignocellulosic product. The lignocellulosic fiber product can be paper and paperboard originating from wood, flax, cotton, hemp, jute and bagasse and can be achieved through different pulping processes. The strengthening agent is achieved through treating a phenolic polysaccharide obtained from potato, corn, waxy corn, wheat, rice, sorghum, waxy sorghum, sago arrowroot or tapioca with an oxidizing agent that catalyzes the oxidation of the phenolic groups. The patent publication discloses in more detail the following types of polysaccharides that could possibly be applied: a) The phenolic polysaccharides such as phenolic starches and phenolic cationic starches are achieved through derivatization of the “parent starch”, b) Phenolic celluloses into which phenolic substituents has been introduced, c) Phenolic polysaccharides derived from polysaccharides of the following types: pectins, galactomannans (guar gum or locust bean gum), arabinogalactan (from western larch timber), dextrans, acacia gum, xanthan gum, tragacanth gum and carrageenan. The phenolic polysaccharides disclosed in this publication are not obtained from wood tissues that are important in the pulp and paper industry, but mostly from cereal crops (monocotyledons) used in the food industry. Xylans and mannans obtained from wood (conifers and eudicotyledons) are not described. The patent application does not describe the use of the polysaccharides in barrier film production.
The U.S. Pat. No. 6,232,101 describes a method for the production of a gelling agent for aqueous liquids for foodstuff, medical/medicinal or agricultural/horticultural applications intended for ingestion. The polysaccharide that contains phenolic hydroxyl groups intended for this application is obtainable from cereals (e.g. hemicelluloses from wheat or maize flour or bran) or from a plant that is a member of the family Cheniopodiaceae (e.g. pectins from sugar beet pulp). The phenolic hydroxyl groups are oxidized and the gelling phenomenon occurs. The produced material can exhibit excellent liquid-absorption and liquid-retention properties. The use of wood derived polysaccharides is not described nor is the use of the pro duct for material applications.
The international patent application WO2004/083256 teaches how to prepare food products, such as emulsions and foams by covalently linking combinations of a protein, a glyceride and a polysaccharide that contain covalently bonded phenolic residues. The polysaccharides (arabinoxylans and pectins) are obtained from sugar beet and cereals and they were thoroughly described by Lex Oosterveld, Carbohydrate research 300, 179-181, 1997 and thesis Lex Oosterveld, Landbouwuniversiteit Wageningen Netherlands, Dec. 15, 1997, ISBN 90-5485785-4. It is to be noted that these polysaccharides are obtainable from cereals and sugar beets and not from wood and the application areas does not include material applications.
US patent application US2009311752 describes a technique for treating hydrolysates of lignocellulosic biomass with phenol oxidizing enzymes such as laccase in order to enhance growth of microorganisms that are sensitive to the inhibitory compounds in the biomass originating from lignin. There is disclosed the neutralization of monomeric, phenolic inhibitory compounds by, for instance, laccase treatment in the lignocellulose biomass after hydrolysis.
In general the documents reviewed above describes the use of the phenolic polysaccharides in the preparation of strengthening agents for pulp, gelling agents, medical/medicinal or agricultural/horticultural applications, emulsions and foams but not for the preparation of material products for i.e. packaging applications, neither is described the purification of polysaccharides from a mixed solution by utilizing the crosslinking method. Even more importantly the described polysaccharides in the above mentioned publications are mostly obtained from various agricultural crops (such as ferulated arabinoxylans, pectins and aromatic starches) that are well known to contain bound aromatic moieties. Wood hemicelluloses (mannans and xylans) and especially those derived from the process waters of pulping processes are not described.
In the prior art there is still a need to solve the problem with industrial production of high molecular weight mannans and xylans derived from wood (that are not derivatized). In the prior art there is also the problem with contamination of hemicelluloses by lignin. In the prior art there is further a problem how to separate mixtures of hemicelluloses with and without bound aroma tics groups.